The response of growing pigs to dietary protein

The response of growing pigs to a range of dietary protein contents was both simulated and measured over a 12-w period from 74 d of age. Six dietary protein concentrations of 0.7 to 1.2-times the TOPIGS recommended levels were used during four growth phases. Amino acid balance remained the same throughout. Responses were simulated using an established growth model. A total of 264 TOPIGS TN60 boars and 264 gilts were reared separately in 48 pens (11 pigs per pen) in a trial conducted at Baynesfield Estate, South Africa. Growth rate and feed intake were simulated and measured weekly, and cold carcass weight (CCW) and P2 were both simulated and measured on each individual. Weight gain increased with dietary protein in boars both in silico and in vivo, whereas gains on all but the lowest protein diet remained constant in silico. A small increment in gain was measured in the trial as protein content increased. Simulated feed intakes were constant in gilts on the four highest protein contents, increasing on the two lowest contents. In boars, intake increased as protein content decreased. No marked trends in feed intake were observed. CCW decreased exponentially as protein content decreased. Margin over feed cost peaked at a higher protein content in boars than in gilts and was influenced to the same extent both in silico and in vitro by changes in the cost of protein-containing ingredients. Uniformity in body weight within treatments increased linearly with dietary protein content.